To make it easy to change direction of travel, casters are sometimes attached to transport devices such as baby carriages or to objects to be moved.
FIG. 1 is a diagrammatic view of a baby carriage having a push rod that can be switched between a back-to-face push mode and a face-to-face push mode. The front wheels of the carriage are provided with casters to permit a swiveling motion. The illustrated baby carriage 1 comprises a pair of front legs disposed on opposite sides and rotatably supporting front wheels 2 secured to the lower ends of the front legs by axles 6, a pair of rear legs 5 disposed on opposite sides and rotatably supported rear wheels 4 secured to the lower ends of the rear legs by axles 7, and a push rod 10. The push rod 10 is tiltably installed so that it can be switched between a back-to face push mode and a face-to-face push mode. The position of the push rod 10 shown by a solid line in FIG. 1 corresponds to the back-to-face push mode, and the position of the push rod 10 shown by a phantom line corresponds to the face-to-face push mode.
Casters 8 are attached to the lower ends of the pair of front legs 3. Each caster 8 is turnable around a rotational axis 9 and rotatably supports the respective front wheel 2 by the horizontal axle 6 at a position horizontally spaced from the rotational axis 9.
In the case where the baby carriage 1 is operated for travel on a smooth surface road in the back-to-face push mode, the axles of the front wheels 2 are positioned rearwardly of the rotational axes 9 of the casters 8 as viewed in the direction of travel. When the direction of travel of the baby carriage 1 is changed, the casters 8 suitably swivel to facilitate the change of the direction of travel. Thus, the provision of casters 8 on the baby carriage 1 improves its in operability.
The manner of switching the push rod 10 from the solid line state shown in FIG. 1 to the face-to-face push mode to operate the baby carriage 1 for travel in this mode will now be described. When the push rod 10 is switched to the face-to-face push mode as shown by the phantom line in FIG. 1 and the baby carriage is operated for travel in this mode, the casters 8 swivel through 180 degrees until the front wheels 2 assume the phantom line position. In this state, the axles 6 of the front wheels 2 are positioned rearwardly of the rotational axes 9 of the casters 8 as viewed in the direction of travel. On the other hand, the rear wheels 4 positioned forward as viewed in the direction of travel cannot swivel. Therefore, when the baby carriage 1 is operated for travel in a face-to-face push mode, the direction of travel cannot be changed so easily.
Most of the baby carriages now on the market have the construction shown in FIG. 1. In other words, when the baby carriage is operated for travel in the back-to-face push mode, the casters act effectively, allowing a smooth change of direction of travel, but when the push rod is switched to the face-to-face push mode, the rear wheels which are now positioned forward as viewed in the direction of travel cannot swivel, so that the direction of travel cannot be changed smoothly.
To solve, this problem, both of the front and rear wheels could be provided with the function of a caster. FIGS. 2 and 3 are diagrammatic views showing a baby carriage 1 with a push rod 10 that can be switched between a back-to-face push mode and a face-to-face push mode and the front and rear wheels 2 and 4 of which are both swivelable by casters 8 and 11. In FIG. 2, the push rod 10 is in the back-to-face push mode, while in FIG. 3 it is in the face-to-face push mode. Each front wheel 2 is supported by a caster 8 which is swivelable around a rotational axis 9, while rear wheel 4 is supported by a caster 11 which is swivelable around a rotational axis 12.
When the baby carriage 1 is operated for travel in the back-to-face push mode as shown in FIG. 2, the axles 6 of the front wheels 2 are positioned rearwardly of the rotational axes 9 of the casters 8 as viewed in the direction of travel. Likewise, the axles 7 of the rear wheels 4 are also positioned rearwardly of the rotational axes 12 of the casters 11 as viewed in the direction of travel.
When the push rod 10 is switched from the state shown in FIG. 2 to the face-to-face push mode and the baby carriage is operated for travel in this mode, as shown in FIG. 3, the casters 8 and 11 are turned through 180.degree.. Therefore, as shown in FIG. 3, the axles 6 of the front wheels 2 are positioned rearwardly of the rotational axes 9 of the casters 8 as viewed in the direction of travel, and the axles 7 of the rear wheels 4 are positioned rearwardly of the rotational axes 12 of the casters 11 as viewed in the direction of travel.
Any baby carriage of the construction shown in FIGS. 2 and 3 has a better operability than the baby carriage of the construction shown in FIG. 1 because in FIGS. 2 and 3 both the front and rear wheels 2 and 4 are swivellable by the casters 8 and 11, whereas in FIG. 1 only casters 8 are provided.
Even the baby carriage shown in FIGS. 2 and 3, however, has problems, because by permitting the front and rear wheels to swivel, these wheels become too sensitive to the unevenness of a rough road surface. Referring to FIG. 4, when the baby carriage is to be moved straight as shown by a solid line A, it responds to the unevenness of the road surface with such a sensitivity that the path of travel of the baby carriage 1 becomes zigzag as indicated by a dotted line B. Referring to FIG. 5, when the baby carriage is to travel along a curved path as indicated by a solid line C, the wheels also respond to the unevenness of the road surface with such a sensitivity that its path of travel becomes zigzag as indicated by a dotted line D.
To operate the baby carriage for travel in a stabilized manner, the zigzag movement described above must be avoided. To this end, it is necessary to provide means for inhibiting the swiveling of the wheels which are positioned rearward as viewed in the direction of travel.